1. Field of the Invention
The present invention generally relates to a recording medium on which data is recorded and a device for recording data on and reading data from the recording medium and, more particularly, to an optical recording medium on which data is recorded and read using more than one recording and reading method and a device which uses more than one method recording data on and reading data from the recording medium method.
2. Description of the Related Art
Image filing systems are widely used as business machines for recording and reproducing document data. In these image filing systems, image data is optically read from a document and recorded onto a recording medium. The image data recorded onto the recording medium may then be read therefrom and subsequently reproduced on a display unit for visual presentation or supplied to a printer to produce a hard copy.
Optical disk devices in these image filing systems use optical disks to record and store the image data. Image data is recorded in tracks on the surface of the optical disk. An optical head of the optical disk device records data on and reads data from the optical disk. The optical head is positioned close to the optical disk and is driven by a linear motor for linear motion in the radial direction of the optical disk.
Three recording and reading methods have been developed to record and read image data on an optical disk. These methods are the constant angular velocity (CAV) method, the constant linear velocity (CLV) method, and the modified constant angular velocity (M-CAV) method. In the CAV method, the angular velocity of the optical disk is maintained at a constant value in order to stabilize the recording and reading operations and to reduce access time. In the CLV method, the angular velocity of the optical disk changes as the optical head is moved radially above the surface of the optical disk in order to maintain a constant linear velocity of the optical disk with respect to the optical head. Thus, the CAV method lends itself to the production of high density optical disks. In the M-CAV method, the angular velocity of the optical disk is set to a constant value. The frequency of a system clock is then varied in accordance with the position of the optical head such that data is recorded along the tracks of the optical disk with a predetermined constant spacing therebetween. In the M-CAV method, the frequency of the clock is increased as the optical head moves radially outwardly in order to reduce access time and increase recording capacity.
Recently, optical disk devices have been developed which can record data on and read data from an optical disk using different recording and reading methods. For example, Japanese Patent Disclosure (Kokai) No. 59-157873 discloses an optical disk device which uses both the CAV method and the CLV method. U.S. Pat. No. 4,896,311, incorporated herein by reference, discloses an optical disk device which uses both the CAV method and the M-CAV method. In these optical disk devices, an operator can select the recording and reading method as desired.
However, conventional optical disks have data recorded on and read therefrom using only one recording and reading method. Thus, it is necessary to change the optical disk each time an operator selects and changes the method for recording and reading dam.
Optical disk devices used in the image filing systems record image data on the optical disk. Recently, optical disk devices have been developed which can record code data when the optical disk device is used as a recording device for a personal computer or a word processor. However, the memory capacity of the optical disks differ from each other with respect to the recording of image data and the recording of code data. However, the recording area of conventional optical disks is divided into a plurality of blocks having equal data storage capacities of, for example, 256 bytes, 512 bytes, 1024 bytes or 2048 bytes. Therefore, it is necessary to change the optical disk used for each purpose.